Tuesday, September 30, 2014
 

Disable JavaScript execution from console

Most modern browser today offers developer tools either as part of browser engine (like Chrome Developer Tools in Google Chrome) or as extension mechanism (like firebug in Mozilla Firefox). These tools are certainly in a way responsible for making JavaScript a much matured language because they provide a powerful tool to debug through the script. Those shortcut keys (F8, F10, F11 etc), which use to work in powerful IDEs, was almost a privilege to other programming languages have finally arrived to JavaScript developers. Matter of no debate, powerful debugging tools is a mandate for any programming language to become mature enough to attract wide audience from developer community.

However as the debugging, which is open for all (remember, it is attached to browser and not to a particular IDE), gets more and more popular, anyone can write script snippet using console and get it executed in the host application environment (i.e., the web page which is being displayed in the browser). Obviously this cannot be considered as security threat since the user who is trying to execute any script snippet has execution permission. For example, if user has no permission to view account statement for other user, he/she cannot do so via executing script using console since the permission are governed by backing server code.

In certain cases, it is still possible that you may want to disable any kind of script execution via console for your web application due to business demands. For the practical reason, neither you can configure user’s browser to disable console nor ask them to stop using console (both won’t work, billions of user and why would they listen to you?)

In such case, the only practical possibility would be to host code in your web application which disallows any script execution via console. Wow! First question, is that even possible? How?

Yes, that’s kind of possible and which is what I am going to explain now. Let’s take example of Google Chrome Developer tools.

Chrome developer tools takes anything which is typed in to console as an input and simply passes it to evaluate function to run it in the host application environment. Before doing so, they create a property “_commandLineAPI” in console object and whole script gets executed in with block as

with ((window && window.console && window.console._commandLineAPI) || {}) {
// your script here.
}

Now seeing what we have above, it is very easy to say that the only way to stop execution of “script code typed in console” is to throw an exception before that.

A simplest way would be to save the console object in a function variable and define console property in window object with accessor/mutators (i.e., get/set). In get function, we could simply check if the property attached by chrome developer tool exists and if yes, throw exception (obviously which is not handled by anyone and hence stops execution of further code).

Here’s the full code snippet

<script type="'text/javascript'">
(function(){
 
    var _z = console;
    Object.defineProperty( window, "console", {
	get : function(){
	    if( _z._commandLineAPI ){
		throw "Sorry, Can't exceute scripts!";
            }
	    return _z; 
	},
	set : function(val){
	    _z = val;
	}
    });
 
})();
</script>

With the above script added in your web application, try launching console and execute any script. You would notice the following message in console (and yes, typed in script in console did not get executed!)

Script Execution Using Chrome Developer Tools

Whoa!!!

 

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Comments: 5

(comments are closed)

 
  • This doesn’t work for me, i have jQuery library and my owns scripts with functions and a lot of stuff, but with this solution that you provide, I’m still able to execute my code in Chrome’s console. And other question, this solution is supposed to work with all the jQuery functions too?.

    Thanks, this post is great, it has a lot of useful information

     
     
     
  • Wow, now it works, thanks a lot. I put that code in the correct place now, inside the $(function…) jquery ready function. Thanks, this is so useful for me, the chrome’s console is very useful for development, but in production, you can do everything you want with javascript, and I didn’t like that.

    Thanks, grettings from Chihuahua MX.

    Isaac Ojeda.

     
     
     
  • Thanks Issac.

     
     
     
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  • [...] last post, I mentioned how to disable JavaScript execution from Chrome Developer Tools and now we’ll have a [...]

     
     
     
 
 

 

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